Currently commercialized secondary batteries include nickel cadmium batteries, nickel hydrogen batteries, nickel zinc batteries, lithium secondary batteries, etc. Compared to the nickel-based secondary batteries, the lithium secondary batteries rarely have the memory effect and thus are freely rechargeable or dischargeable, have a very low self-discharge rate, and have a high energy density.
The lithium secondary batteries generally use lithium-based oxide and a carbon material as a positive electrode active material and a negative electrode active material, respectively. The lithium secondary battery includes an electrode assembly in which a positive plate and a negative plate coated with the positive electrode active material and the negative electrode active material are provided by disposing a separator therebetween, and a housing, i.e., a battery case, for sealing and accommodating the electrode assembly together with an electrolyte.
In general, depending on the shape of the housing, the lithium secondary battery may be divided into a can-type secondary battery in which the electrode assembly is accommodated in a metal can, and a pouch-type secondary battery in which the electrode assembly is accommodated in a pouch made of an aluminum laminate sheet.
Secondary batteries are broadly used not only in small devices such as portable electronic devices but also in medium or large devices such as vehicles or power storage devices. When used in the medium or large devices, a large number of secondary batteries are electrically connected to increase capacity and output. Particularly, pouch-type secondary batteries are easily stackable on one another and thus are commonly used in the medium or large devices.
However, the pouch-type secondary battery is generally wrapped by a battery case made of a laminate sheet of aluminum and polymer resin and thus has a low mechanical strength. Accordingly, when a battery module including a plurality of pouch-type secondary batteries is configured, cartridges are used in many cases to protect the secondary batteries from external impact, to prevent motion of the secondary batteries, and to easily stack the secondary batteries on one another. The term “cartridge” is interchangeable with various other terms such as “frame”. A plurality of cartridges are stacked on one another to configure a battery module, and secondary batteries may be located in empty spaces generated when the cartridges are stacked on one another.
When a plurality of secondary batteries are assembled using a plurality of cartridges as described above, plate-shaped cooling fins, i.e., cooling plates, may be provided between the secondary batteries. The secondary batteries may be used in a hot environment, e.g., summer, and may autonomously generate heat. In this case, if a plurality of secondary batteries are stacked on one another, the temperature of the secondary batteries may be further increased. If the temperature is increased beyond a proper temperature, the performance of the secondary batteries may deteriorate and, even worse, the secondary batteries may explode or burn. Therefore, when a battery module is configured, cooling plates may be provided between the secondary batteries to prevent an increase in temperature of the secondary batteries.
The battery module in which the cooling plates are provided between the secondary batteries may cool the secondary batteries in various manners. As a representative cooling method, an air cooling method for reducing the temperature of the secondary batteries by making the external air flow near the cooling plates to exchange heat between the cooling plates and the air. In the battery module for cooling the secondary batteries using the air cooling method, the air may flow into and out of the battery module by providing cooling channels near the cooling plates and connecting the cooling channels to ducts.
In general, a cooling plate may be made of metal such as aluminum and a part other than the cooling plate, e.g., a frame, may be made of a material such as plastic. The above-described cartridge for secondary batteries may be manufactured using various methods. Representatively, insert injection molding may be used. Based on insert injection molding, the cartridge may be manufactured by preparing a cooling plate and then injection-molding a frame body while the cooling plate is in an insert injection molding machine.
However, using the above-described manufacturing method, the cooling plate may be deformed due to contraction of the frame body. That is, when a cooling process from a high temperature to a low temperature is performed during insert injection molding, the injection-molded frame body may contract more than the cooling plate. For example, in the cooling process, a frame body 1 may contract as shown by arrows in FIG. 1.
A cooling plate 2 is generally configured as a thin plate. If the frame body 1 contracts as described above, the cooling plate 2 may not resist the contraction of the frame body 1 but may be deformed or distorted. Due to the deformation or distortion, a cooling channel may not be stably ensured and thus a cooling effect may be greatly reduced.
Furthermore, a pouch-type secondary battery may generate a harmful gas during operation. In this case, the harmful gas may leak through a gap between the cooling plate 2 and the frame body 1 and flow into the cooling channel. For example, in an electric vehicle, air in a cooling channel of a battery pack may flow out of the battery pack into an air circulation duct of the vehicle and the air of the air circulation duct may flow into the vehicle. As such, if the harmful gas flows into the cooling channel, the harmful gas may flow into the vehicle and damage health of people in the vehicle. However, the cartridge according to the related art insert injection molding method may not solve the above problem due to unstable sealability between the frame body 1 and the cooling plate 2.